You are correct. The later revision "light grey trim" Atari PC's produced in 1989 had either a 5.25" or a 3.5" as the floppy drive. FYI the earlier "dark grey" revision produced in 1988 (as seen in the other listing) only had a 5.25" as the floppy drive.
I should mention, how nice of that guy to rip the specs right off my website but fail to realise the keyboard he has included is NOT the original Atari XT Keyboard. The original keyboard is Atari branded and has the F1-F12 keys on the left hand side just like the original IBM XT Keyboard.
That guy is a dead set idiot (sorry no nice way to put it). I'm not joking, he's been listing that exact same complete Atari PC3 for YEARS but doesn't get the hint that the price he has listed is way too much in fact it was higher! I tried to reason with him a few years back when I was first looking but despite showing him listings where others had sold for less than 100 euro's (box only I might add but to give him an idea of price) he wouldn't budge. A couple of months later I picked up a complete system almost identical to his (it was a German version not Italian like his) and I think it cost me about 500 all up including shipping from Germany to Australia which in itself wasn't cheap.
Correct, they basically just rebadged the Atari ST peripherals for the PC line. The STM1 Mouse became the PCM1, the SF314 External Floppy became the PCF314 etc.