Can this be a problem on mobile?

I have a long master passphrase - too long to type on a touchscreen keyboard in any convenient amount of time and where there's a non-trivial risk that somebody peering over my shoulder (think - using it on the bus) could spy it. So in that case I resort to using the fingerprint-unlock feature (which I assume is the security equivalent of 'save master passphrase' or at least token).

I am aware that this might open me up to other attacks - an adversary dusting my fingerprints off my tablet, etc. Curious though as to whether this is an attack vector for the same or a similar type of process to what the authors are describing (haven't read their blog post, just the Black Hat description).