Zobo could be correct, but there are other possibilities, as well, the first being that it was just a coincidence. Another alternate and viable explanation to your group of gobblers disappearing at the onset of the breeding season was the lack of hens being there and that they simply went looking to find hens.
Here's another thing that I find perplexing. Rios are pretty vocal, and especially this time of year...and if you were out on your property at first light in the morning, it would be surprising to me that you would not hear them gobbling, even if they were on another property and quite a distance away. If you were out there at that time and couldn't hear gobbling in the distance somewhere, I have my doubts that they could have heard you calling to them and decided to come check it out just coincidentally after you left.
On the other hand, if you have not been hitting the property until later in the morning and gobbling activity may have ceased, they may have been in the general vicinity all the time, heard your calling without responding and/or from a long distance away...and as Zobo says, may have decided to work their way over to take a closer look.
At any rate, it is hard to say for sure...but it sounds like you may now be in the ball game for getting one or more of them now that they are back!