Why is old commits being captured in new PRs?

Question

I created a new Pull Request in GitHub and did one small change and noticed that 66 other changes from the past were captured in that PR.

How do I fix this? Would a rebase help? If so, what kind of rebase?

* 378e690 (HEAD -> dc/removing_index.ts-rebased, origin/dc/removing_index.ts, dc/removing_index.ts) Removed trailing index.ts file
*   db3bf5d (dev) Merge branch 'dev' of github.com:Looney/service-integration into dev
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| *   5d63a87 (origin/dev) Merge pull request #25 from Looney/dc/test_optimization
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* | | 147b446 working on token generation and test potimization
| |/
|/|
* | d5e74b2 Change gendevkeys to make keys dir
* | 39114de Add ability to have js file for jest config
* | 19f9e77 Add bash script to generate keys for dev
* |   e75053a Merge branch 'AR-600/pass-token-to-url-in-response' into dc/test_optimization
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| * | eae6e72 (origin/AR-600/pass-token-to-url-in-response) add readme for .env
| * | ce2bbf6 Remove coverage and add to gitignore
| * | 9b56e4f Refactor to make token generation easier
| * | e5aaa4f Add linter and formatter along with local dev instructions
* | | 1aa8725 working on tests and cleanup
* | | 2886a84 working on getting tests to work with jest
| |/
|/|
* | f7dd2b9 removed swagger commit
* |   57f8632 resolved merge conflict
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| * \   eda2b29 Merge pull request #23 from KnoxMed/wm/f/logger
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| | |/
| |/|
| | * d04c7cf (origin/wm/f/logger, wm/f/logger) fix Winston log file location, gitignore logs directory
| | * 43aac04 add logging
| | * 510fde4 remove duplicate log
| | * a59a995 replace console.log in services with logger
| | * 0d061af replace console.log in /ping with logger, call logResponse from /dashboard
| | * f7e62e4 add logResponse convenience function, replace console.log in /partner with logger
| | * 0ab1140 add convenience log function, replace console.log in /dashboard with logger
| | * d0dc882 change logger output
| | * b9c814c Bring in Winston as logger, configure it, replace console.log in app.ts with logger
| | * 98014f9 Add /api/v3/ping route, update version in package.json
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* / b040b94 working on getting api-docs endpoint rendering
|/
* 476657a (origin/fix_type_definition_errors_for_params) fixed the type definition errors for parameters
* 872c8d0 (origin/wm/b/validate-request) resolve verifyAuth compile error
*   811264a resolved merge conflict
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| * a686181 (origin/dc/f/debugging_start_script) changed number of params in verifyAuth to leave verifyAuth in app.ts as-is
| * 655f573 removed env variables from script,added nodemon,worked on debugging verifyAuth method
* | f307387 fix compile errors in tests (2 errors left)
* | b8aa704 fix compile errors in /partner/*
* | b0e2ff1 fix bug where /partner/* returns 201 when data isn't stored in DB when request body is not an array
|/
* d79eec7 Added production env variables to build script
*   0146e2f fixed merge conflict
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| * 875b2fb (origin/wm/f/dashboard-patient-view) Need to translate V1 id due to V2 pai / pui
| * 95eaec8 more debug log (/dashboard with patientId not working)
| * 8ba0771 add debug logs, update README
| * 84b46b3 add internal-use only APIs to get doctors and delete doctor

So my PR is including everything and much more from above, when I just want commit titled: Removed trailing index.ts file

I created this branch from what would be the "master" branch, in this case it's called dev. Is it that all the work that was merged in that branch is being brought over?