Is 'Burglary' specific to residential property? I thought it was.
No it isn’t, Eddie. Although there is a considerable difference between the two in the sentencing guidelines (with domestic burglary being considered far more serious), as Dave explains, burglary can be committed on either type of property. Here’s a paragraph from the CPS charging guidance:
“The definitions of burglary offences in section 9 of the Theft Act 1968 do not distinguish directly between the burglary of a dwelling or a non-dwelling. There are, however, important differences in respect of venue and sentencing.
Any charge or count on an indictment should therefore specifically plead whether the building is a dwelling or otherwise.”
An important point to note with burglary (and often misunderstood) is that forced entry is not required for the offence to be made out. If a person simply walks through an open door into a building or part of a building where he should not go (provided he has an intention to steal, inflict GBH or commit damage , or actually does so) he is guilty of burglary. This is why I cannot understand the charge the OP’s relative is said to face. By definition, trespassing with intent to steal is burglary.