That builders plate looks like its off a BNSF unit… I’ve never seen a ferromex paint scheme with yellow stripes.
I think what he means is that GE sent this unit down to Ferromex for testing, perhaps to set parameters for the 50 units GE will be building for them… probably in no small part to establish whether Ferromex needs the tier 4 rating for ‘enough’ of their traffic to justify acquiring some. (The other thread on this indicates some good reason why this may be so.)