The title is a little convoluted, so hopefully I can explain better here.
At 9th-level, an Armorer Artificer gets the class feature "Armor Modifications":
You learn how to use your artificer infusions to specially modify your Arcane Armor. That armor now counts as separate items for the purposes of your Infuse Items feature: armor (the chest piece), boots, helmet, and the armor’s special weapon. Each of those items can bear one of your infusions, and the infusions transfer over if you change your armor’s model with the Armor Model feature. In addition, the maximum number of items you can infuse at once increases by 2, but those extra items must be part of your Arcane Armor.
Effectively giving the Artificer three more things they can infuse.
Do the boots and helm count as "A suit of armor" for the sake of infusions?
For instance, the "Armor of Magical Strength" has a prerequisite of "A suit of armor". So if the armor was still considered one piece, you could infuse the armor. But now it's considered four pieces. Can I infuse "Armor of Magical Strength" on say, the boots portion. Or are they now only considered boots and can only be infused with "Boots of the Winding Path"? And the helm can only be infused with "Helm of Awareness"?
The follow up would be, if they are still armor, does that mean a character cannot infuse their special weapon as a weapon?
I found this question, which would suggest that the weapon because a weapon. I'm asking whether boots become boots or are still part of the suit.
It just seems like a crappy feature to say, your armor is now four pieces so you can customize with more infusions. But two of those four can only be two specific infusions and both of them require attunement.
Although, an argument can be made for not only those two infusions, but use the "Replicate Magic Item" to infuse the boots as "Boots of Speed".