Officers spend most of their time writing reports, they're not going to write one if they are not required to do so, depending on their stations policy. Officers also do not like to put too much information in their reports, because many times defense lawyers try to trip them up on the wording and details of the report. They like to keep them as simple as possible.
If the report thing is bothering you, just get a copy of the arrest report of the guys that the cop got after he spoke with you. I highly doubt your name would be on it, more then likely he simply would state he responded to a tip. The report would only support the time and place of the incident for you.
You could also get a recording of the 911 call of the person reporting you.