The shulchan aruch is a “popular Halacha book”. Just saying.
Yes, but the author was an expert on the subject matter :), and followed basic rules (which were broken every now and then) so that everyone could understand where the Halacha was sourced and that he did not make it up using a Boich Svarah. Makes the “book” into a “Sefer”.
These “popular Halacha books” would be Seforim if they actually sourced their Halacha. Then again, if they did, they couldn’t be Machmir 100% of the time (See the differences between R. Falk’s Teshuvos, where he Paskens, and his “book”, where he is Machmir (as per the minhagim of his community), because he doesn’t have to defend a Psak. He can simply say “this is what should be done”. And everyone (even outside his community) does it, or their Isha children get bumped down on the Shidduch list and all their children are rejected from schools as “not following rules” or “not our type” or “not following Halacha”).
</rant>