"Overfeeding deficiency it is very rare in those circumstances as all the material are organic." - this in no way impacts overfeeding or underfeeding... that is about concentration of the various molecules involved (the math does not chage for "organic") not a marketing term. overfeed / underfeed is 100% about math, not a marketing term. (organic as used in horticulture is not a science term.. it is a bastardized science term whose definition was hi-jacked and warped into something grotesquely untrue that preys on people's false perceptions of the natural world.)
Is it some sort of slow release thing? Concentration isn't about how much substrate there is, but rather ho much water the substrate holds... and this varies based on how the substrate is constructed... so this is a flaw in instructions that interjects more volatility than necessary. (better option.. per volume of liquid..)
so is this some sort of top-dress dry feed?
it's too esoteric... this is something you need to learn through trial and error. the little seedling looks fine, though. way too early to tell. t he seedling doesn't need nutes for 7 days from sprout, though a lighter feed than normal can help initially.
with soil it's always a trial and error process... keep track of how you feed and observe results... adjust next time -- too many variables are different in each garden to give exact instructions.