Bang on; Cr-48 was chosen precisely because it's an unstable isotope of chromium.

For a second I thought it was a play on create (Cr348 = Cr-48), but your explanation sounds better.

What the speaker said went along the lines of "after awhile the engineers settled on 48." It seemed like there wasn't a clear reason behind it, although my lack of chem knowledge could be why.

They alluded to something like that in the webcast.

More likely the software engineers were only moderately versed in chemistry (in a didn't do it since high school/college way) and just doubled the atomic number to get the atomic weight, not realizing that for heavier elements more neutrons are required for stability.