It appears its a cross between the two while epdm is solid epdm the liner that is in question here is a weave with epdm saturated . But from the site you provided they said it can be repaired in the same manner as epdm . Do you know how to do a seal ?That's a bad tear there.
I agree, that doesn't look like an EPDM liner. Possibly HDRPE, but that's tough stuff too.