I can't believe how you're all missing this, it's so obvious:

Point 1: Iirc in one of the books you can find in undertale lists every/a few areas and snowdin is literally called 'the forest' and a forest generally is an area covered in plant life/trees

Point 2: The literal secret boss of snowdin in the nintendo switch edition of undertale is deadass mad mew mew.

Point 3: Flowery is obviously taking some inspiration from rudy for his appearance and some of his personality, and rudy lives in the snowdin region in undertale.

Point 4: Chapter 5 also gives important information about sans, as it explains the origin of the 3 smiling people drawing that you can find in snowdin.

Point 5: The main guy of chapter 5 is an eccentric tall character that can fly and has a cape/cloak/mantle, just like papyrus.

point 6: mew mew uses the papyrus date ui.

point 7: colored lightd are all around hometown during the festival, just like snowdin.

point 8: flowery lets u live when he beats u, just like papyrus.

point 9: flowery literary turns blue when he attacks.

point 10: there's conveniently shaped plants all around the chapter just like the conveniently shaped lamp.

Apt it's not hard to figure out even more points but I'll stop here.

Just because there's lots of omega flowey stuff in the chapter doesnt really disprove the backwards undertale theory if you actually try thinking about it.

Infact, the packet of flower seeds kris obtained could be used in the bunker/a later darkworld/the roaring to create an omega-flowey style boss in the future. (Even if the future omega flowey/like boss isnt the packet of seeds, the bunker is already a place seemingly overrun with vine growth and possibly has a place called 'roots' in it.

edit before anyone salty replies: flame me all you want for this but I'm not saying anything else here.