A HUD home is titled very much the same as a car or trailer and a BOCA is not.
A HUD home is built on a steal frame with axles and a BOCA is not.
A HUD home is constructed with 3/8 inch drywall panels with no mud work and all seems are covered with a strip, and a BOCA is constructed with 1/2 inch drywall and mudded the same as a stick built home.
HUD homes are plumbed with cheap plastic tubes and BOCA homes are plumbed with copper pipes or whatever is required by the local building code. 

A BOCA home has a higherpitched roof and some are two story homes such as a Cape Cod style home. 

Many banks will not finance HUD homes but most banks will finance a BOCA home.

When you walk into a HUD home it is very obvious that you are in a HUD home, but a BOCA is not so apparent and you would need to look in the basement or crawl space to inspect the framing of the floor to confirm it is a BOCA and not a stick built home. 

BOCA stands for Building Officials and Code Administrators. 

The BOCA standard is a minimum by which all stick built or site built home builders must comply.