According to this website containing info on strawberry guavas:
The seeds can be eaten carefully or roasted as a coffee substitute.
Apart from that site, I can find no other references anywhere suggesting that a drink can be made from guava seeds. That site doesn't give much detail about how this would be done.
Does anyone know if guava seeds can be used in this way, and if so how to go about it? If you went to all the trouble, would it taste any good? You can dry, roast and grind the seeds of anything but that doesn't mean the end result would make a drink that tastes better than hot sand. My understanding of coffee production is that it is a tricky process to go from the raw beans to the final product so perhaps careful steps need to be followed to make a perfect cup of guava seed?
I am unable to find a single reference to guava seed coffee when searching the internet.
While lack of evidence is not evidence of non-existence, it seems highly unlikely this practice, if it actually exists, is wide spread or well known. It is probably it simply is not true.
I tried making some today with seeds I collected by blending, straining and separating with water. Then roasting using a method I have seen used with coffee beans. Honestly was not that great, it was very weak, I tried a drip method and also french press, but both were very watery. Here Is a short video of what I did, not including the seed separation process. I am sure some coffee roaster is turning over in his grave, I am by no means experienced in this so you may be able to produce better results. https://photos.app.goo.gl/yVKNpwnF5Dpl91fm1 (sorry about vertical video.)