Why the solution notation in Lichess API is different from the pgn (standard) notation ?

Hi all,
I'm developing a chess program and using the Lichess API to play puzzles.
It works fine, however, I'm a bit confused about how the solutions are written down. Piece letters and captures are not mentioned, instead they are replaced with the start position of the piece.
For instance the following moves Rxb7, Qxb7, Nf6 become b1b7, c7b7, e4f6.

Is it the usual way to write down solutions in chess or is it a specific Lichess notation ?

if it meant for computers I guess it used UCI protocol notation, that is what i would use anyway. SAN is bad way to give moves, people make mistakes with while keeping noten in OTB games and sometimes there are two ways to write the move.

g1f3 is easy to parse and impossible to misunderstand.

Thanks for your answer.
In the API the weird thing is the game is given in SAN and the solution in UCI protocol notation.
lichess.org/api#tag/Puzzles
It would have been more logic to me to give both in the same notation.
Anyway, thanks again.