Strangles test

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I'm having a vetting done in half an hour and the vet called me to say that they have found that at a previous yard the pony was at a year ago there was a possible undiagnosed case of strangles but nothing was ever confirmed. Apparently another horse had arrived at the yard, information here unclear, the horses that already lived there including the one I am looking at were all given 2 blood tests 3 weeks apart. All horses were established not to have strangles, but the one I am looking at had an antigen result of 0.3 each time, which puts him in the borderline results category. The vetting vet wants to know if I want a guttural pouch test doing to see if he is a carrier. I'm not sure which way to go forward with this. Has anyone got any experience of this sort of thing? In all the time I've been buying horses I've never been asked this question. Further info, the pony has moved livery yards during the last year with no infections.

In an attempt to understand what the results of a blood test mean, I've been having a little search and came up with this from a vet surgery's web page. The pony was 0.3 at his first test and 0.3 at his second test, so no rise in antibodies suggesting he hadn't been infected by the horse they were suspecting, but there's no explanation for why he would have any antibodies:

"A negative result (≤0.2) for both antigens indicates the animal is unlikely to be a carrier and or have been exposed to S.equi 2 weeks prior to the sample being taken.
A borderline result (0.3 – 0.4) to either antigen indicates the animal may have recently been exposed to S.equi. We recommend a repeat blood sample 10-21 days later to look for a rising titre.
A positive result (≥0.5) to either antigen indicates further testing is recommended – either testing guttural pouch washes (by culture and/or PCR) or examination of three repeat nasopharyngeal swabs."

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Stand down - he was never in contact with a suspected strangles case. It was a test taken as a precaution.