It means a 386 that was IBM-compatible, presumably.
Not sure there were all that many 386 systems that weren't, though I'm sure they exist...
A UK company called Jarogate had a line of 386 based CP/M machines that didn't use an IBM PC compatible architecture.
CMOS versions of the 386 also showed up in some mobile phones and other embedded systems.
IBM 386? Did they mean to say Intel 386, or did Linus actually have a computer that used an IBM 386SLC, which was an 80386 that IBM designed and manufactured under license from Intel?