lawinsider defines grooming as: "befriending and establishing an emotional connection with an individual to lower the one's inhibitions for emotional, physical, or sexual abuse."
Pedophilia is a term used to describe a sexual attraction to pre-pubescent children younger than 12. Sexual behaviour is also not required, just as someone straight or gay can know their orientation without any interaction.One is a sexual attraction towards a specific age, whilst the other is merely an action that anyone can experience, and is not inherently sexual.
The takeaway is that you acknowledge pedophiles may be groomers, but not all groomers are pedophiles.
Denji is introduced as a 16 year old within the start of the manga - he is a teenager - not a child; Makima also has zero sexual attraction towards Denji, therefore this also does not qualify as valid criteria for pedophilia…