Bc of what us HUMANS have done to the pittie breed, there
are some pitties and pittie traits that can be unpredictable and aggressive. Many/most pitties are just big 'ol goobers who think they are lap dogs though
. But human beings have altered the natural course of this poor breed - and we now see the consequences of what we've done.
But the real issue here is not to just be careful bc this is a pittie...the real issue is to be extra, extra careful bc 1) another dog is involved (*any* dog) and 2) it's a larger dog. *Any* two dogs can be very dangerous to each other if they get triggered; if a big and small dog get dangerous together, it's most likely going to be the smaller dog who pays dearly. Also, a large dog can - through no real fault of its own - end up hurting a small dog just from trying to innocently play w/ a smaller dog.
With Chewie being small (aka more vulnerable) AND aggressive, you should approach this w/ extreme caution. Keep both of them on leash for a good long while during introduction - and you only allow them off leash if they do not trigger each other. If either one triggers the other, you need to be careful and keep them separated or leashed to you at all times.