Are standard 20A receptacles a NFPA 58 ignition source?
This doesn't apply to you, but...
As of the 2017 edition (with no sign of changes in 2020), NFPA 58 Table 6.25.2.2 sets a 15' (not 10'!) distance between unclassified (ordinary location/non-ignitionproof) electrical equipment and the filling ports of containers over 1000lb water capacity.  However, NFPA 58 6.25.2.4 waives that requirement for commercial and residential installations:

6.25.2.4 The provisions of 6.25.2.2 shall not apply to fixed
electrical equipment at residential or commercial installations
of LP-Gas systems or to systems covered by Section 6.26.

Personally, though, I would keep receptacles out of the 15' radius around the fill port anyway; this is a mitigation against the risk of someone plugging in unrated portable electrical equipment that could serve as an ignition source in its own right, though.