It's the battery that loads the alternator output if not near fullly charged, so a measured voltage below the regulated 14.3 or so volts is entirely to be expected given the situation. I do wonder if the regulator has become intermittent though so it may happen again!
Once battery is fully charged suggest keeping a regular eye whilst driving on running battery volts. Expect no less than 14.2 -14.4 volts. Hopefully the Li-ion battery is of the type with internal regulation to adjust to batteries differing charge needs.
