There are different weight mods (MTOW/MZFW) for Metro 3, without knowing for sure operating weights and payload it is hard to estimate whether a fuel shortage could have been a factor. Metro fuel burn is quite low for its speed (ca 250 kgs/hour) so depending of the weights it could have anything between low fuel or enough fuel to divert as far as Gatwick.
10 pax range is something like 1200 nm + standard reserves with an average weight specs.