This is actually wrong. Today there is unfortunately nothing that prevents a snap that plugs pulseaudio from recording via pulseaudio. Ubuntu Touch had a patched pulseaudio that used trust-store which would perform contextual prompting to enforce the distinction, but this work was not upstreamed and is therefore not available with snaps on classic distro. The pulseaudio snap for Ubuntu Core could be patched for this, but I don’t think it is since there is no mechanism to prompt in the cli environment (@morphis could correct me here). There is a portal in the works for pulseaudio, but it isn’t upstream: add a sound portal · Issue #27 · flatpak/xdg-desktop-portal · GitHub.
As for ALSA, please see @ogra’s comment. pulseaudio is a sound server that snaps should use since accessing ALSA devices directly will cause multiplexing issues for a lot of chipsets. Some specialized snaps might want direct access to ALSA devices (eg, jackd), so it exists for them. In terms of recording and playback, there is no difference between the two: both allow both.