Yes, I would think those things could look similar, but I think we can tell them apart.
The history is probably the biggest key,
A haematoma would require trauma or anticoagulation.
An abscess would be a very sick, febrile and septic patient.
In these cases there was just progressive calf swelling.
Another clue is that a calf tear of medial gastroc doesn’t happen at this location. They always tear from the aponeurosis deep to the muscle. I have not seen a tear that sits just under the superficial muscle fascia. When I see fluid here I think of a Bakers cyst extension.
Also, you can carefully track the collection back to a neck which terminates at exactly the right spot for a Bakers cyst between medial gastroc and semimembranosus.