Query regarding buy back

Extract from FM Book by Khan & Jain
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I think confusion is arising because in debt to equity ratio sometimes long term debt is used instead of total liabilities as a numerator.
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But generally, current liabilities should be included because
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1) Current liabilities also form the part of debt and one of a factor determining the risk taking appetite of a firm.
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2) Major component of current liability is short term bank loan, which also carries interest cost with it.
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3) Short term creditors restrict the management activities as they have to be paid on time.
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Hence without including this, we may not be able to assess the correct solvency position.