Why not just say from scratch instead of no prior experience, is it to brag

Might be intended to preemptively deflect criticism of "reinventing the wheel"/solving subproblems in a non-standard/convoluted way.

I'd expect an engineering project with "no prior experience" to take weird/experimental approaches more often compared to a "from scratch" project (where I would expect proven minimalism instead).

"from scratch" and "no prior experience" have very little in common.