I had a guy approach me in a gas station and advise me - in this country I should ride on the hard shoulder.

He passed me before and objected to having to change lanes to go around me. I'm doing 100-120kmh and overtaking cars and trucks on my left hand.

He described the blue sign ( which is information ) it says for bikes 'use the shoulder' - As its a dual carriageway in Thailand there's oncoming traffic and cars that pull out without looking in addition to scooters plodding along at 60 kmh.

I thanked him for his concern and will not be running in the gutter, but I was just interested in anyone else's interpretation of this sign.

It's Thailand. Road signs, lights, and even markings are recommendations and not rules...unless it's pay the gik/mia nois time for the BiB.

I'm surprised you were approached; unless it was a farang that is uncharacteristic of the population.

Sounds like a bellend. Ignore him and ride wherever it's safest.

I thought it meant return to the left hand lane once your overtaking manouver is completed , as in England. Ride where you feel safest is the best advice. Unusual you were approached.

Ask him if he would like to sit pillion for a while so he can understand how illogical it is to force riders to reduce their safety options. Hold on, something wrong with that picture... tip of my tougue... That's it, I should think about road-stuff with my small head and only in the light of my convenience and maintenance of perceived status...

If he wanted to pass you and you didn't move to the left to let him by (forcing him to pass you on the left instead of the right), I understand his point- I don't like scooters in my way in the right lane either (not that I mind if they use it, but a rider in that lane needs to be conscious of what's going on behind him and not just sit in the passing lane without realizing he's often going to be a roadblock, even if he's riding 100kph+). Whether you were overtaking cars to your left makes no difference- you need to make room for faster traffic.

If you were on the right side of the left lane, then the driver really should have let it go if all he had to do was change lanes and pass you on the right (it's not clear from your OP)- legally he's correct and you should have been on the left side of the left lane to let faster traffic go by without their having to change lanes, but practically you were in the correct position.

Which was it?

^ Maybe it's terminology but in the uk the hard shoulder referred to is the small left hand lane for breakdowns and emergency vehicles where all the crap is (not the most left car lane - the bit to the left of that), the equivalent in Thailand is the small lane where bikes turn into the traffic towards you. Where dogs hang around to take a pi. Glass, cans etc.

I admit to using it to overtake when it's clear/clean and there's no space on the right but to suggest that is where bikes belong is pretty silly IMO.

I agree with staying left if not overtaking, assuming it's not rutted, soaked in truck diesel or covered in crap.