Glue up strategy was pipe clamps alternating on top and bottom every foot. I also used biscuits.
Alternating clamps top and bottom is a good way to help achieve a flat glue-up, but if you want to be absolutely sure you need to actually clamp the top flat somehow. You can do this with individual clamp pressure at each joint being glued (using just a C-clamp or with a purpose-made clamping accessory) or do it across the entire span using a caul.
Some related info in these previous Answers:
What is a good way to prevent jointed tabletops from bowing when tightening fasteners or the glue sets?
Not-so-obvious disadvantages of butt joints
FYI biscuits to nothing to help panels stay flat (and they don't add strength). They're merely an alignment aid in this sort of jointing.
Could the bow be because of over tightening the pipe clamps?
I don't think so if you alternated clamps. Definitely a possible cause if you hadn't done this though.
Brief note on clamp pressure: with a joint like this which relies completely on the glue bond for strength you actually do want to clamp hard. The clamp pressure should be sufficient to squeeze out all the excess glue, which in practice means you want to clamp hard enough that you're forced to use scrap blocks to prevent denting of the edges by the clamps. If you've done your edge jointing well this sort of clamping pressure will result in glue joints so thin you can't see them — minimum standard you should aim for is not being able to seem them at arm's length, if you're more discerning they should be completely invisible no matter how closely you look.
What else could have contributed to the bow?
Clamping the glue-up flat with further clamps may not have prevented this from occurring however because I suspect acclimation may have been at least partially the cause.
Wood not ready
Regardless of how long the pine sat in your workshop prior to you using it if you planed it down to final thickness in one go (especially if from one side more than another, or one side only) and then used it quickly that could have directly led to it warping unfortunately.
It's a much better strategy if time allows to plane down partially to thickness, putting the wood aside (stickered, and with heavy weights on top) to acclimate again, and then after a few days or longer planing off the last 1/8" (3mm) or so to get down to final working thickness. This gives the exposed core of a plank, which is generally slightly damper than the wood at the surface, time to get down to equilibrium with the working environment in stages, rather than all in one go.
Not quite square
Another possible cause is an ever-so-slight discrepancy in the squareness of the edges, which after the glue has dried and the clamps are removed makes its presence known. Far less than half a degree is enough for a bow to be generated. So if you're not 100% certain that your edge jointing results in a perfect 90° edge it's a good idea to joint each pair of mating boards in alternate directions, that is, one face in to the fence and the next face out. This way any slight angle difference is cancelled out — see diagram here for clarity. The drawing relates to hand-jointed edges but the same principle applies to edges jointed by machine.
