Here is a brief insight into how messy medical billing is...
As others have said, the first doc was almost certainly a fellow (licensed, completed pediatric residency, now doing subspecialty training in pediatric gastroenterology). Possibly a resident, but less likely considering the clinic you were at. Second doc is almost certainly the attending/supervising physician who would do the billing.
Consult - This has noting to do with the fact that a second Dr. came into the room. It is just a billing code that means your primary doc referred them for assessment/recommendations from a specialist, and the specialist then sent a letter to that referring provider explaining their assessment and recommendations.
If you see a code 99241-99245 on your bill, that means consult. For what it's worth, this code has been phased out by Medicare and maybe some other insurers. If you see a code 99041-99045, then the code is initial office visit ("Evaluation and Management"), rather than consult.
The billing comes down to either how many items they have checked off (asked about or examined, and documented in their note) in three categories - History, Exam, and Medical Decision Making. Or, alternatively, they can bill based on time spent, if over half the time was spent on "counseling and care coordination" which basically means discussing the diagnosis, and treatment options.
If you really wanted to, you could ask for a copy of the note (you might have to pay for it) and sit down with someone who understands medical coding. It is very common for docs to not realize that they are billing a level higher than what their documentation actually supports. If the last digit in the level of service is a 4, but should only be a 3, you may save $100 or so. I doubt you would save much more than that.
Finally, there is also a facility fee added since you went to a clinic that is part of a hospital. This can be pretty exorbitant, and likely accounts for a very large portion of that $900. There was a big lawsuit in Seattle about a decade ago because some clinics affiliated with (but not attached to) a hospital were submitting $900 charges, after facility fees, for clipping toenails of diabetic patients in a dermatology clinic. There is probably nothing you can do about the $900 part
The system is very broken in many ways. Above is just a bit of the mess that goes into determining bills for visits - and a big part of what drives all of the time wasted doing paperwork and unnecessary charting and bloating of elctronic medical record systems. Most of us in medicine get it wrong a lot of the time, because it is so messy.
For what it's worth, this system was invented by the AMA (a system which strongly favors surgical and procedural specialties over non-surgical specialties in terms of charges), and is abused on all sides by health care providers, hospitals, and insurers, fighting back and forth over dollars.
This is one of the huge problems that the ACA didn't really address, and one of the things that needs to change before we can have more efficient pricing in medical care.