Got the ol' Mackey in my head. "Fencehopping is bad, m'kay? You shouldn't do fencehopping."
Sigh. But since we know people are going to do it anyway regardless of what we advise...
Goat's probably on the right track. My guess is its probably normal discharge consistency for that individual dog . They have to pass unfertilized eggs at the end of the cycle, so that may be what you saw, and blood does of course clot naturally so if this was 'old' blood and not quite fresh, ie. got hung up somewhere and did not fully evacuate the vagina until hours later, that could be why it was clumpy. Could be mucous material too. When I was a young man in my 20s working at a shelter/vet clinic, I thought I had worms once from all the patient clean-up duties -- til I described it to one of our on-staff vets and she reminded me there's mucous in shit, lol. The more you know! She did give me a sample collection container just in case, har har. Ditto consider the similar process for diagnosing presence of blood in stools: your vet will invariably ask first whether it was bright red (fresh) or dark and tarry (even black), appearing as though it had dried. If its the former fresh red, your animal has an injury or condition low in the rectum somewhere; if its black you've got something going on further up the GI tract that had time to work its way thru, drying out by the time it was passed with the stool. Rule of thumb for discharges around my ranch from various species, is I use my nose. Next time sniff it -- if it smells foul, it could be infected material. Then you look for corroborating symptoms eg. fever, lethargy, off-feed, excessive thirst or no thirst, swelling/pain in an affected area, etc.
Perhaps the other guys who've owned bitches longer than me can chime in as I'm no expert; my knowledge of normal vs abnormal bitch discharge is limited. I've had males most of my life, don't breed (not dogs anyway, just livestock), and could probably tell you more about cattle / sow estrus than canine. But, if it'll help with perspective and peace of mind, in my time I've had several female dogs come thru my ranch on temporary/foster stays eg. an older rottie who'd birthed a few litters in the past, a young shepherd mix who'd never whelped, two danes who were both in heat when they were here, and a husky ditto in heat while she was here. In all of them, heat or not, I've observed small trace amounts of discharges (often with presence of dark/old blood but not always) that I chalk up to background-normal excretions for intact females. Likewise for my current mastiff girl, who came to me as a rehome off a puppy mill and is still with me but very old (7-8, about the end of the line for giant breeds). She's had god-knows how many litters bred thru her from the previous owner. She, same as the others (who were younger), also has occasional 'background' leaks/discharges but is otherwise healthy, normal, and asymptomatic of anything. And as I recall the bloody stuff even went on for awhile after her last heat. Though hers is never coagulated/clotted, pretty runny and dark actually. I myself am curious what that is, but it resolved on its own in time. As I said my knowledge in this area is limited, so hopefully the guys who've owned intact bitches longer than me can chime in with their observations.
Hope that helps with perspective anyways.