If you make two separate transactions, one from each address, then the answer is more complicated. If both transactions are to the same deposit address, and that address can easily be identified as belonging to an exchange, then that is a fairly strong indication that the same person controls both addresses
Why?

I don't follow that logic.
You could have easily told Person A to send funds directly to your exchange deposit address... and also told Person B to send funds directly to your exchange deposit address. Just because two addresses have sent to the same address, there is no reason to tag them as "probably" belonging to the same person, even if the destination is an exchange deposit address.
Basically, it's like saying "AddressA sent to AddressC" and "AddressB sent to AddressC" so A and B are "alt accounts". That's proof of nothing other than A and B sent funds to C. There is no way to definitively determine the relationship between A and B, without extra information being available.