The hot grease caused bodily harm to the victim. Considering the sentence he could have received, I don't think he was punished too harshly.
Criminal Code
PART VIII: OFFENCES AGAINST THE PERSON AND REPUTATION
Assaults
Assault
265. (1) A person commits an assault when
(a) without the consent of another person, he applies force intentionally to that other person, directly or indirectly;
(b) he attempts or threatens, by an act or a gesture, to apply force to another person, if he has, or causes that other person to believe on reasonable grounds that he has, present ability to effect his purpose; or
(c) while openly wearing or carrying a weapon or an imitation thereof, he accosts or impedes another person or begs.
Application
(2) This section applies to all forms of assault, including sexual assault, sexual assault with a weapon, threats to a third party or causing bodily harm and aggravated sexual assault.
Consent
(3) For the purposes of this section, no consent is obtained where the complainant submits or does not resist by reason of
(a) the application of force to the complainant or to a person other than the complainant;
(b) threats or fear of the application of force to the complainant or to a person other than the complainant;
(c) fraud; or
(d) the exercise of authority.
Accused’s belief as to consent
(4) Where an accused alleges that he believed that the complainant consented to the conduct that is the subject-matter of the charge, a judge, if satisfied that there is sufficient evidence and that, if believed by the jury, the evidence would constitute a defence, shall instruct the jury, when reviewing all the evidence relating to the determination of the honesty of the accused’s belief, to consider the presence or absence of reasonable grounds for that belief.
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Criminal Code
PART VIII: OFFENCES AGAINST THE PERSON AND REPUTATION
Assaults
Assault
266. Every one who commits an assault is guilty of
(a) an indictable offence and is liable to imprisonment for a term not exceeding five years; or
(b) an offence punishable on summary conviction.
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Criminal Code
PART VIII: OFFENCES AGAINST THE PERSON AND REPUTATION
Assaults
Assault with a weapon or causing bodily harm
267. Every one who, in committing an assault,
(a) carries, uses or threatens to use a weapon or an imitation thereof, or
(b) causes bodily harm to the complainant, is guilty of an indictable offence and liable to imprisonment for a term not exceeding ten years or an offence punishable on summary conviction and liable to imprisonment for a term not exceeding eighteen months.
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http://www.canlii.com/ca/sta/c-46/sec265.html