Well, technically it does have a full service history in that there is a full history /record of what's been serviced. However, it clearly doesn't have a full service history in accordance with the manufacturer's service schedule; it's a play on words and is certainly not within the 'spirit' of what people generally expect FSH to mean.How long have you had the car, and who arranged and paid for the third service - was it the previous owner/keep or a trader/dealer? Perhaps the previous owner knew they intended to sell soon after and so had the bare minimum service done in order to say it had been serviced every year, likewise a trader wanting to sell with maximum margin might do the same.
It certainly hasn't got a Full Service History without the spark plugs, automatic transmission fluid and differential fluid changed. Unfortunately I've seen this far too many times when looking at secondhand cars. Once a car is older than 2 years old it's unusual to find a car which really has had all scheduled service actions performed. Service plans are growing in popularity which should help.
Unfortunately, it seems to be something that is cropping up more and more often and highlights the need to check invoices against the 'record'. I'm often amazed at how some relatively expensive cars are 'run' by 'owners' who scrimp on basic servicing requirements, possibly not surprising when some people find out how expensive some fairly basic service items can now be.
The best service record I've seen (years ago) in a car was a 10-year old Bentley, for sale af a franchised RR dealer, that had been sent back to the factory, by its only owner, every 3-months for servicing and came complete with several fully-stamped service books (remember those?) and supporting invoices. The car was immaculate and I initially thought that it done 30,000 miles but closer inspection revealed 130,000 miles. I digress.