Bubble Memory "IBM 256KB Memory Card" P/N 6407740 ?

There was some debate at VCF East whether this "IBM 256KB Memory Card" P/N 6407740 is a bubble memory card (pic below). The card was on display with my IBM PC 5150 exhibit. I originally pulled it from an IBM 5155 portable. http://www.vintagecomputer.net/ibm/5155/ibm_256KB_memory_card_6407740.jpg Typically you don't see 32-pin 64K RAM chips on a ISA card. That does not make it bubble memory though, so I put this out to the esteemed CCTECH community for answers/ideas. I do not have a technical reference manual, but I do have the IBM 64/256KB Memory Expansion Option manual. That ain't it. Date codes on some of the chips are from 1984. The memory chips are marked 6119927 IBM-14 PQ ESD 1 H28 708016 I found this from a web search for IBM 6407740: IBM-14 PQ ESD 64KB 32-PIN MEMORY MODULE 5150/5175 ...so, whadda we gots ? Thanks Bill