Rulings
Q1: Does this card's digivolution requirement where it can digivolve from a Tamer mean that the Tamer that will become a digivolution card is treated as a Digimon when it digivolves?
No, it digivolves from the Tamer as-is.
Q2: When a Tamer would digivolve using this card's digivolution requirement, is it considered a Digimon that would digivolve?
No, it isn't considered a Digimon that would digivolve. When a Tamer would digivolve using this card's digivolution requirement, "when a Digimon would digivolve" effects don't trigger.
Q3: When a Tamer digivolves using this card's digivolution requirement, is it considered a Digimon that digivolves?
No, it isn't considered a Digimon that digivolves. When a Tamer digivolves using this card's digivolution requirement, "when a Digimon digivolves" effects don't trigger.
Data Sources
Lv.4 Grumblemon BT18-012 C Hybrid | Variable | Demon [Digivolve] [Gigasmon]: Cost 0 [On Play] [When Digivolving] Delete 1 of your opponent's Digimon with 3000 DP or less. --- Inherited: [When Attacking] [Once Per Turn] Delete 1 of your opponent's Digimon with 3000 DP or less.
Lv.4 Grumblemon BT18-012 C Hybrid | Variable | Demon [Digivolve] [Gigasmon]: Cost 0 [On Play] [When Digivolving] Delete 1 of your opponent's Digimon with 3000 DP or less. --- Inherited: [When Attacking] [Once Per Turn] Delete 1 of your opponent's Digimon with 3000 DP or less.
Lv.4 Grumblemon BT18-012 C Hybrid | Variable | Demon [Digivolve] [Gigasmon]: Cost 0 [On Play] [When Digivolving] Delete 1 of your opponent's Digimon with 3000 DP or less. --- Inherited: [When Attacking] [Once Per Turn] Delete 1 of your opponent's Digimon with 3000 DP or less.
Lv.4 グロットモン BT18-012 C ハイブリッド体 | ヴァリアブル種 | 鬼人型 「ギガスモン」:コスト0 【登場時】【進化時】DP3000以下の相手のデジモン1体を消滅させる。 --- Inherited: 【アタック時】[ターンに1回]DP3000以下の相手のデジモン1体を消滅させる。