Why one dog's snack doesn't spread the risk
Sunflower seeds aren't contagious like a toxin or allergen would be — what one dog ate has no bearing on the other's health. Your 8 kg dog's consumption only matters for his own digestive system. The seeds' fat content might give him slightly softer stool, but this won't affect his housemate through shared bowls or contact.
The real separation needed would be if the seeds had shells, which could pose a physical hazard. Since these are shelled, there's no risk of one dog passing sharp fragments to the other through saliva or food remnants. Their bowls can stay together unless the eating dog starts guarding seed-related items aggressively.
How a tablespoon affects an 8 kg dog differently than a larger one
At his size, that tablespoon of seeds represents a more significant fat intake than it would for a giant breed. His pancreas may need to work harder to process the sudden oil influx, potentially leading to one or two loose stools. This isn't dangerous unless he's prone to pancreatitis, which you didn't mention — just something to note if his digestion seems off.
Unlike with toxic foods, the amount he ate won't accumulate in his system or leave residues that could harm his companion. The other dog's avoidance is irrelevant unless the seeds were a choking hazard (unlikely with shelled ones). Their future meals need no adjustment based on this single incident.
The 24-hour window for noticing digestive changes
If the seeds will bother him, you'll see signs within a day — most commonly a single episode of soft stool or slightly decreased appetite. These are mild reactions that resolve without intervention. Only if he vomits, becomes lethargic, or refuses multiple meals should you consider veterinary input. His 8 kg size makes dehydration from diarrhea slightly more concerning than in a larger dog, but that's unlikely from this small amount.
Compare his behavior to his baseline: a normally voracious dog skipping one meal is less alarming than a picky eater refusing food. Neither scenario links back to the other dog's bowl, since the seeds' effects are contained to whoever ate them. Track his water intake more closely than his housemate's for the next day.
Why separating bowls isn't the solution
Food aggression or resource guarding would be the only valid reasons to separate their bowls after this incident — not the seeds themselves. The eating dog might show temporary interest in seed-like foods, but that's a training issue, not a medical one. Unless he starts seeking out unsafe foods, their shared meals can continue as usual.
If you're worried about future scavenging, train both dogs equally rather than dividing their space. The seeds didn't create an imbalance between them; they just highlighted which dog is more opportunistic. That trait matters more for preventing other incidents than for managing this low-risk one.
The full verdict, portion guidance and serving notes are collected on the Sunflower seeds food facts page.